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Remove the poorly-designed reduce_512 API

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Unused and unpublished. This was only added in the FCMP++ branch as a quick fix
for performance reasons. Finding a better API is still a tricky question, but
this API is _bad_.
This commit is contained in:
Luke Parker
2025-08-19 15:24:33 -04:00
parent cfd1cb3a37
commit ca85f9ba0c
5 changed files with 0 additions and 38 deletions
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6
crypto/ciphersuite/src/dalek.rs
View File

@@ -28,12 +28,6 @@ macro_rules! dalek_curve {
$Point::generator()
}
fn reduce_512(mut scalar: [u8; 64]) -> Self::F {
let res = Scalar::from_bytes_mod_order_wide(&scalar);
scalar.zeroize();
res
}
fn hash_to_F(dst: &[u8], data: &[u8]) -> Self::F {
Scalar::from_hash(Sha512::new_with_prefix(&[dst, data].concat()))
}

6
crypto/ciphersuite/src/ed448.rs
View File

@@ -66,12 +66,6 @@ impl Ciphersuite for Ed448 {
Point::generator()
}
fn reduce_512(mut scalar: [u8; 64]) -> Self::F {
let res = Self::hash_to_F(b"Ciphersuite-reduce_512", &scalar);
scalar.zeroize();
res
}
fn hash_to_F(dst: &[u8], data: &[u8]) -> Self::F {
Scalar::wide_reduce(Self::H::digest([dst, data].concat()).as_ref().try_into().unwrap())
}

16
crypto/ciphersuite/src/kp256.rs
View File

@@ -31,22 +31,6 @@ macro_rules! kp_curve {
$lib::ProjectivePoint::GENERATOR
}
fn reduce_512(scalar: [u8; 64]) -> Self::F {
let mut modulus = [0; 64];
modulus[32 ..].copy_from_slice(&(Self::F::ZERO - Self::F::ONE).to_bytes());
let modulus = U512::from_be_slice(&modulus).checked_add(&U512::ONE).unwrap();
let mut wide =
U512::from_be_bytes(scalar).rem(&NonZero::new(modulus).unwrap()).to_be_bytes();
let mut array = *GenericArray::from_slice(&wide[32 ..]);
let res = $lib::Scalar::from_repr(array).unwrap();
wide.zeroize();
array.zeroize();
res
}
fn hash_to_F(dst: &[u8], msg: &[u8]) -> Self::F {
// While one of these two libraries does support directly hashing to the Scalar field, the
// other doesn't. While that's probably an oversight, this is a universally working method

6
crypto/ciphersuite/src/lib.rs
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@@ -62,12 +62,6 @@ pub trait Ciphersuite:
// While group does provide this in its API, privacy coins may want to use a custom basepoint
fn generator() -> Self::G;
/// Reduce 512 bits into a uniform scalar.
///
/// If 512 bits is insufficient to perform a reduction into a uniform scalar, the ciphersuite
/// will perform a hash to sample the necessary bits.
fn reduce_512(scalar: [u8; 64]) -> Self::F;
/// Hash the provided domain-separation tag and message to a scalar. Ciphersuites MAY naively
/// prefix the tag to the message, enabling transpotion between the two. Accordingly, this
/// function should NOT be used in any scheme where one tag is a valid substring of another

4
crypto/dkg/promote/src/tests.rs
View File

@@ -29,10 +29,6 @@ impl<C: Ciphersuite> Ciphersuite for AltGenerator<C> {
C::G::generator() * <C as Ciphersuite>::hash_to_F(b"DKG Promotion Test", b"generator")
}
fn reduce_512(scalar: [u8; 64]) -> Self::F {
<C as Ciphersuite>::reduce_512(scalar)
}
fn hash_to_F(dst: &[u8], data: &[u8]) -> Self::F {
<C as Ciphersuite>::hash_to_F(dst, data)
}